| dc.identifier.uri | http://hdl.handle.net/11401/77646 | |
| dc.description.sponsorship | This work is sponsored by the Stony Brook University Graduate School in compliance with the requirements for completion of degree. | en_US |
| dc.format | Monograph | |
| dc.format.medium | Electronic Resource | en_US |
| dc.language.iso | en_US | |
| dc.publisher | The Graduate School, Stony Brook University: Stony Brook, NY. | |
| dc.type | Dissertation | |
| dcterms.abstract | The composition and thermal structure of the Earth’s mantle, especially the mantle transition zone, still remain controversial due to the lack of direct access to the Earth’s interior. An important geophysical approach to constrain the mineralogical composition of the mantle is to compare seismic profiles (e.g., PREM and AK135) with the elasticity of candidate compositional models calculated by averaging schemes based on the phase equilibrium and elasticity data of individual mantle minerals. However, chemical reactions, element partitioning and diffusion cannot be fully taken into account by this approach. In this study, I conducted direct velocity measurements on KLB-1 peridotite which is compositionally close to pyrolite up to the pressure and temperature conditions of the mantle transition zone. The KLB-1 specimens were successfully hot-pressed at mantle conditions followed by X-ray diffraction, optical and scanning electron microscopy (SEM), electron probe micro-analyzer (EPMA) analyses on specimens for a full characterization before conducting the ultrasonic measurements at high pressure. For the off-line acoustic measurements, we developed a new method for in-situ pressure determination in multi-anvil, high-pressure apparatus using an acoustic travel time approach within the framework of acoustoelasticity. It not only can be used for continuous in-situ pressure determination at room temperature and high temperatures, during both compression and decompression, but also for simultaneous pressure and temperature determination with a high accuracy (±0.16 GPa in pressure and ±17 ºC in temperature). Comparison of the P and S wave velocities of a KLB-1 specimen at room temperature with Voigt-Reuss-Hill (VRH) calculations based on literature elasticity data for its constituent minerals indicates that the experimentally measured P and S wave velocities, densities, bulk sound velocities and VP/VS ratios fall close to the lower limit of VRH averages within the uncertainties of the mineral elasticity data. Mantle temperatures under western North America have been estimated from a comparison between the velocities of KLB-1 specimens measured at mantle conditions and the TNA2 shear velocity model to be along a 1450 ºC adiabat or along a 1300-1350 ºC adiabat after correction for the effect of inelasticity. The velocity jump at 410 km is 6.6% for P wave and 7.0% for S wave with a volume fraction of 70% for olivine. A Lehmann discontinuity is observed at the pressure of 7.5-7.8 GPa (230-240 km) with the velocity jump of ~1.5% and velocity-pressure slope change for P and S waves, which may be caused by the large mineral compositional change before and after this pressure. Our results also suggest that the temperatures in the mantle of this region are beneath the solidus and the velocity reduction does not require the presence of partial melt beneath this region. | |
| dcterms.abstract | The composition and thermal structure of the Earth’s mantle, especially the mantle transition zone, still remain controversial due to the lack of direct access to the Earth’s interior. An important geophysical approach to constrain the mineralogical composition of the mantle is to compare seismic profiles (e.g., PREM and AK135) with the elasticity of candidate compositional models calculated by averaging schemes based on the phase equilibrium and elasticity data of individual mantle minerals. However, chemical reactions, element partitioning and diffusion cannot be fully taken into account by this approach. In this study, I conducted direct velocity measurements on KLB-1 peridotite which is compositionally close to pyrolite up to the pressure and temperature conditions of the mantle transition zone. The KLB-1 specimens were successfully hot-pressed at mantle conditions followed by X-ray diffraction, optical and scanning electron microscopy (SEM), electron probe micro-analyzer (EPMA) analyses on specimens for a full characterization before conducting the ultrasonic measurements at high pressure. For the off-line acoustic measurements, we developed a new method for in-situ pressure determination in multi-anvil, high-pressure apparatus using an acoustic travel time approach within the framework of acoustoelasticity. It not only can be used for continuous in-situ pressure determination at room temperature and high temperatures, during both compression and decompression, but also for simultaneous pressure and temperature determination with a high accuracy (±0.16 GPa in pressure and ±17 ºC in temperature). Comparison of the P and S wave velocities of a KLB-1 specimen at room temperature with Voigt-Reuss-Hill (VRH) calculations based on literature elasticity data for its constituent minerals indicates that the experimentally measured P and S wave velocities, densities, bulk sound velocities and VP/VS ratios fall close to the lower limit of VRH averages within the uncertainties of the mineral elasticity data. Mantle temperatures under western North America have been estimated from a comparison between the velocities of KLB-1 specimens measured at mantle conditions and the TNA2 shear velocity model to be along a 1450 ºC adiabat or along a 1300-1350 ºC adiabat after correction for the effect of inelasticity. The velocity jump at 410 km is 6.6% for P wave and 7.0% for S wave with a volume fraction of 70% for olivine. A Lehmann discontinuity is observed at the pressure of 7.5-7.8 GPa (230-240 km) with the velocity jump of ~1.5% and velocity-pressure slope change for P and S waves, which may be caused by the large mineral compositional change before and after this pressure. Our results also suggest that the temperatures in the mantle of this region are beneath the solidus and the velocity reduction does not require the presence of partial melt beneath this region. | |
| dcterms.available | 2017-09-20T16:53:10Z | |
| dcterms.contributor | Li, Baosheng | en_US |
| dcterms.contributor | Liebermann, Robert | en_US |
| dcterms.contributor | Wen, Lianxing | en_US |
| dcterms.contributor | Holt, William | en_US |
| dcterms.contributor | Walker, David . | en_US |
| dcterms.creator | Wang, Xuebing | |
| dcterms.dateAccepted | 2017-09-20T16:53:10Z | |
| dcterms.dateSubmitted | 2017-09-20T16:53:10Z | |
| dcterms.description | Department of Geosciences | en_US |
| dcterms.extent | 163 pg. | en_US |
| dcterms.format | Monograph | |
| dcterms.format | Application/PDF | en_US |
| dcterms.identifier | http://hdl.handle.net/11401/77646 | |
| dcterms.issued | 2016-12-01 | |
| dcterms.language | en_US | |
| dcterms.provenance | Made available in DSpace on 2017-09-20T16:53:10Z (GMT). No. of bitstreams: 1
Wang_grad.sunysb_0771E_12901.pdf: 5361386 bytes, checksum: 8d11943f6555dae4e7009c0c8670bd54 (MD5)
Previous issue date: 1 | en |
| dcterms.publisher | The Graduate School, Stony Brook University: Stony Brook, NY. | |
| dcterms.subject | Elasticity, KLB-1 peridotite, Mantle composition, Mantle temperature, North America, Velocity | |
| dcterms.subject | Geophysics | |
| dcterms.title | Mantle composition and temperature of western North America revealed from in-situ velocity measurements of KLB-1 peridotite | |
| dcterms.type | Dissertation | |
